Such a general running gear has been previously described in East German Letters Patent DD-PS 84 511. The disposition of a tandem running gear on a combine has the advantage that the permissible structure width, which is determined by the road traffic regulations, can be used to a great extent for the threshing and sifting device, because the drive wheels located behind each other require less lateral space than dual wheels, but offer the same amount of contact surface with the ground. Furthermore, an increase in the contact surface can be attained by providing the pairs of wheels with track chains, which is advantageous in wet areas, for example in rice fields.
It had been proposed to dispose the swing arm of the tandem drive in a freely movable manner when in the fields by giving the hydraulic lift cylinder a by-pass or short circuit control between its lift chambers. For road travel it was intended to pivot the tandem arm by means of the hydraulic work cylinder in such a way that only the front pair of wheels or the middle pair of wheels had contact with the ground. The wheel drive for the two pairs of drive wheels was provided via drive chains from the tandem axle or via individual hydraulic drive motors. In this way it was possible for all wheels to make a contribution to forward movement corresponding to their ground contact. In the over-the-road position it was proposed to disconnect the free wheel pair from the drive. The incomplete use of the structure width between the two tandem wheels was disadvantageous, because in addition to the wheels, the tandem arm was also disposed on the side of the combine chassis. Another disadvantage was the lack of regulation of the wheel loads.
A combine is also known from German Utility Model DE-GM 71 01 995, the drive wheels of which were disposed on the front in a tandem arrangement. It was provided here that only one pair of wheels of the tandem wheels was directly driven. The drive between the pairs of wheels was provided by a track chain running around them.